Bass runs? scales? Your objective is to learn 'How to do bass runs?' For my theory, to make it simple,(i don't know about the others), Bass is basically people relates to ROOT. Do you mean like, when you play while you are singing, you want to perform a bassline together with a rythmic line? First you gotta know the root of any chords. Second, learn what chords are made of? Third, learn more about 'bass' skills and there are variety of bass line you can learn if u r more to bass. Eg. When you play the normal chord C major where the root is , say take any of it.. 5th string on the 3rd fret. When you play a 4/4 beat, you probably play C-C-G-G-C-C-G-G (this is the bassline where you play bass G on the 6th string 3rd fret but your chord remains C major. Hope this gives you the basic idea. This is just the basic part. If you want the complicated stuff, try get into Fingerstyle where you will play all the lead line, bass line and the rythm line... which is of course, a step higher than this. Hope this helps...